The invention relates to the field of electric motor assembly. More specifically, the invention relates to a method for setting a bearing gap in an electric motor.
Disc drive memory systems have been used in computers for many years for storage of digital information. Information is recorded on concentric memory tracks of a magnetic disc medium, the actual information being stored in the form of magnetic transitions within the medium. The discs themselves are rotatably mounted on a spindle. The information is accessed by using read/write heads generally located on a pivoting arm that moves radially over the surface of the disc. The read/write heads or transducers must be accurately aligned with the storage tracks on the disc to ensure proper reading and writing of information.
During operation, the discs are rotated at very high speeds within an enclosed housing by using an electric motor generally located inside a hub that supports the discs. One type of motor in common use is known as an in-hub or in-spindle motor. Such in-spindle motors typically have a spindle mounted using two ball or hydrodynamic bearing systems to a motor shaft disposed in the center of the hub.
In a hydrodynamic bearing, a lubricating fluid such as air, gas or oil provides a bearing surface between two relatively rotating members, typically a shaft and surrounding sleeve. A volume containing the lubricating fluid is typically capped with a bearing counterplate. The counterplate is positioned proximate an end of the shaft and is spaced from the shaft by a small gap. To effectively form hydrodynamic bearings, the volume must be consistently and accurately formed. As such, the gap between the counterplate and the shaft must be repeatable from disc drive to disc drive in the manufacturing process.
Therefore, there is a need in the art for setting a gap for a hydrodynamic bearing using an accurate and repeatable method.
An apparatus and method for setting a gap in a hydrodynamic bearing of a disc drive spindle motor is provided. The invention comprises placing an end of a shaft into shaft support aperture in the hub, fitting a thrust bearing counterplate into a recess defined by an annular retaining flange that is proximate the end of the shaft, and deforming the counterplate to form a gap between the end of the shaft and a surface of the counterplate.
In one embodiment of the invention, the method for setting a gap comprises assembling a spindle motor having a rotor hub with the thrust bearing counterplate affixed to the top, an axial shaft and a radial bearing for the shaft. After the components of the motor are assembled, a ring is press fit into a recess defined by an annular retaining flange formed in the rotor hub that is annularly disposed about the thrust bearing counterplate, the press-fit ring squeezes the thrust bearing in the rotor hub. The pressure exerted on the thrust bearing counterplate causes the counterplate to deform outward from the center to its ends. The distortion of the thrust bearing creates a gap between the thrust bearing counterplate and the rotor shaft. The gap created is both precise and repeatable.
In another embodiment of the invention, the method for creating a precise gap in a hydrodynamic bearing comprises assembly of a press fit ring to a recess in a rotor hub before assembling the thrust bearing counterplate. The thrust bearing counterplate is pressed fit in place and laser welded to the rotor hub. After welding, the counterplate to the rotor hub, the press fit ring is removed. The removal of the press fit ring creates a tensional force that causes a tortional effect in the thrust bearing. The tortional effect is significant enough to produce a gap similar to that of the first embodiment and is also both precise and repeatable.
In yet another embodiment of the present invention, the method for creating a precise gap in a hydrodynamic bearing comprises assembly of the rotor hub, including but not limited to, assembly of the shaft and bearings in the rotor hub. After the thrust bearing is assembled, it is laser welded in place. This laser welding is different than that of the previous embodiment. In this embodiment, the laser""s depth and penetration of both the hub and the bearing material is much greater. After the weld is completed, the assembly is allowed to cool. During the cooling process, the previously welded material begins to shrink. This contraction of the material causes tensional forces to be exerted on the thrust bearing counterplate. As cooling increases, tensional forces increase until a plastic deformation occurs in the thrust bearing counterplate and a gap is formed between the shaft and the thrust bearing counterplate. As in the previous embodiments, the gap created is both precise and repeatable.
This invention is especially useful in disc drive spindle motors having hydrodynamic bearing motors, in that it provides a more effective and efficient way of assembling hydrodynamic bearings and disc drive spindle motors. Additionally, the invention may be useful for setting gaps in hydrodynamic bearings of other types of motors.